Why don't you start by thinking of something you are genuinely interested in and curious about. Try to answer a question you have always wondered about. Interesting projects come from your passion and innovation. I agree that you want something measurable.

In choosing a science fair project, try to pick something that you have a basic understanding about. You want to test the relationship between two factors, known in scientific terms as the independent variable and the dependent variable. You basically think the availability of one variable influences the other, such as the amount of sunlight plants receive has an impact on how much they grow.

Other ideas worthy of consideration would be the effect of temperature on water dissolving sugar; the effect of mass on force generated; the effect of acceleration on force generated; the effect of density on bouyancy. All these ideas demonstrate the relationship between the two factors called the independent variable and the dependent variable. Virtually anything that you think causes something else is testable in the form of an experiment and would make a great science fair project.

I would suggest always doing a project that allows you to collect measurable data that can be shown in graphic format. Some projects may require this but if yours does not then I would include it anyway because a graph is easy to read and makes a project board look nice. Some ideas I have are as follows: